1. Field of the Invention
The present invention relates to developing apparatuses which are used in image forming apparatuses, such as copying machines and printers, for developing electrostatic images on image holding members, and also relates to developer regulating members used in the developing apparatuses.
2. Description of the Related Art
Developing of electrostatic images on image holding members with powdery toner as developer has been practically performed. In a developing apparatus for this type of developing, an amount of toner on a developing sleeve is regulated by a regulating blade. The developer regulating blade generally comprising a elastic plate is fixed above a developing sleeve in a developing container and is flexibly pressed into contact with a surface of the developing sleeve in a direction opposite to the rotation direction of the developing sleeve. The toner thickness on the developing sleeve is regulated to form a thin toner coating layer by passing through a nip section between the developing sleeve and the regulating blade, and is triboelectrically charged to develop a latent image by friction with the nip section.
Rubber and metal plates have been used as regulating blades. Rubber regulating blades exhibit inferior durability due to plastic deformation caused by aging over long periods of use. Metal regulating blades are extremely difficult to adjust so that the blade comes in contact with the developing sleeve and the toner thereon with a suitably low contact pressure.
Japanese Unexamined Patent Publication No. 6-258,926 discloses a multilayer regulating blade shown in FIG. 6, which includes an elastic layer 4a composed of rubber or the like and a supporting layer 4b composed of a thin metal plate, which supports the elastic layer 4a at the longitudinal end along the transverse direction. The elastic layer 4a on the regulating blade 4 comes in contact with the developing sleeve surface to regulate an amount of toner on the developing sleeve, and the supporting layer 4b on the regulating blade 4 controls the flexibility of the regulating blade 4 and thus the contact pressure of the elastic layer 4a on the developing sleeve. A regulating blade that includes a supporting layer and an elastic layer which have different functions has been effectively used.
However, new toner development trends toward finer particles and sharp melting characteristics require new technology for forming a thinner toner layer on a developing sleeve with further reduced contact pressure between the regulating blade and the developing sleeve. Light contact of the regulating blade 4 can be achieved by decreasing bending strength (stiffness), which is defined in "Method of Bond Test for Metallic Materials: JIS Z2248, push bending test", of the supporting layer 4b composed of, for example, a metal foil, of the regulating blade 4. A decreased bending strength of the supporting layer 4b, however, causes the supporting layer 4b to be less durable and thinner or softer. Since the supporting layer 4b is more elastic with decreased bending strength, the elastic layer 4a cannot be evenly provided on the supporting layer 4b, and thus the surface of the elastic layer 4a at the side in contact with toner is not smooth. Therefore, the regulating blade 4 does not regulate to uniformly apply the toner on the developing sleeve 4, and irregular image density and white lines result. Accordingly, the supporting layer 4a of the conventional regulating blade 4 requires a large bending strength.